1-beta-D-arabinofuranosylcytosine is the most effective agent in the treatment of human acute myelogenous leukemia. The mechanism(s) of action of ara-C and the basis for selectivity against leukemic cells, however, remain unclear. This agent incorporates into leukemic cell DNA. The extent of (ara-C) DNA formation correlates with inhibition of DNA synthesis and loss of clonogenic survival. Moreover, inhibitory effects of the incorporated ara-C residue are related to the sequence of the DNA template. While previous studies showed that ara-C results in the accumulation of DNA fragments, recent findings have demonstrated that this agent induces DNA cleavage at multiples of approximately 200 base pairs. This pattern of internucleosomal DNA fragmentation has been observed during programmed cell death. Recent studies have demonstrated that treatment of human myeloid leukemia cells with ara-C is associated with induction of the c-jun early response gene. The finding that related genes coding for leucine zipper transcription factors are similarly activated at the transcriptional level has suggested that ara-C induces a program of specific gene expression. Further studies are now needed to determine the signalling mechanisms responsible for ara-C-induced activation of these and other early response genes. Moreover, the finding that specific gene expression is induced by ara-C in association with internucleosomal DNA cleavage provides new insights into the cellular response to the effects of this agents. These issues will be addressed in the proposed work. The specific aims are: 1) To determine the effects of ara-C on patterns of early response gene expression; 2) To study the regulation of c-jun and other early response gene expression by ara-C; 3) To examine the involvement of protein kinases in signalling pathways activated by ara-C; 4) To determine the effects of ara-C on internucleosomal DNA cleavage and induction of a programmed cellular response; and 5) To study the in vivo formation of (ara-C) DNA in leukemic myeloblasts and the potential for selectively inhibiting incorporation of ara-C into DNA of hematopoietic stem cells.